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Responses of sheep to annual cycles in nutrition 1. Rôle of endogenous growth hormone during undernutrition

Published online by Cambridge University Press:  02 September 2010

N. R. Adams ,
J. R. Briegel ,
R. D. G. Rigby ,
M. R. Sanders  and
R. M. Hoskinson
N. R. Adams
Affiliation:
CSIRO Division of Animal Production, PO Wembley WA 6014, Australia
J. R. Briegel
Affiliation:
CSIRO Division of Animal Production, PO Wembley WA 6014, Australia
R. D. G. Rigby
Affiliation:
CSIRO Division of Animal Production, Blacktown, NSW 2148, Australia
M. R. Sanders
Affiliation:
CSIRO Division of Animal Production, PO Wembley WA 6014, Australia
R. M. Hoskinson
Affiliation:
CSIRO Division of Animal Production, Blacktown, NSW 2148, Australia
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Abstract

Plasma concentrations of growth hormone (GH) are elevated in sheep during undernutrition. The present study attempted to determine whether this increased secretion mediated nutritional effects on reproduction or wool growth, using sheep immunized against growth hormone-releasing hormone and given a low-quality, sub-maintenance diet. Immunization reduced plasma concentrations of GH at all times measured (P < 0·01), through reduced pulse frequency, reduced pulse amplitude, and reduced baseline concentrations. Plasma insulin-like growth factor-1 (1GF-1) was also reduced in the immunized sheep (P < 0·01). Despite this, rates of live-weight loss and wool growth were similar in immunized and control ewes. Plasma concentrations ofLH and FSH were also similar in immunized and control ewes, both during the late luteal phase and after ovariectomy and supplementation with oestradiol and progesterone. Numbers of ovarian follicles and corpora lutea were also unaffected by immunization. It is concluded that high endogenous concentrations of GH in sheep given food below maintenance are necessary to maintain plasma IGF-1, but do not affect the concentration of gonadotropins or ovarian follicular growth. Furthermore, rates of live-weight loss and the depression in wool growth in such animals were also independent of concentrations ofGH or IGF-1.

Keywords

reproductionsheepsomatotropinundernutritionwool
Type
Research Article
Information
Animal Science , Volume 62 , Issue 2 , April 1996 , pp. 279 - 286
Copyright
Copyright © British Society of Animal Science 1996

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References

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